Wreck, I don't know too many people who actually work on the machines who trust ID mics. I have a couple of sets myself, and despite the fact that they are correct as close as I can adjust them, I still have a habit of measuring over them as though they were telescoping gages. So that's hardly uncommon.
And on your big mics, even stacking gage blocks can be suspect. The general preference is to have a one piece standard that is factory made, and having it calibrated to an
actual size by an NIST lab in QC, controlled environment and used for checking the big mandrel mics. Very rarely are they as close as most people think they are. I have sets up to 24", and calibrated standards for each inch. They're not current, because I haven't needed them in a long time and to spend money on an annual cal would be ridiculous. If I need them, and I am required to back them up, I'll have the standards re-certed, but not until I can justify it. And yes, I can run my entire shop at 68°f and 50% RH, just as though it were a inspection/calibration room. I have a certified thermometer with hygrometer on the wall to prove it if I need it. NOT at the moment, thank goodness.....this broken leg is really beginning to bug me!
I think the point being made is that there are times when it is a matter of maintenance rather than actual damage. Most all dial calipers have a spring loaded pinion gear to "jump" over any trash that may (read:will eventually) get in the rack. That's why they send the little copper tool to reset it. No biggie, and no damage to the calipers at all.
I'm not picking on you, honest!